Overview
Primary angle closure glaucoma (PACG) is an important cause of glaucoma worldwide, especially in East Asia, and the leading cause of bilateral glaucoma blindness in countries such as Singapore, India, and China. Recent population-based surveys have shown that PACG is most commonly an asymptomatic disease, and the visual morbidity of the condition may be related to the finding that the asymptomatic form of the disease is visually destructive.
Clinical background
Under the International Society for Geographical and Epidemiological Ophthalmology (ISGEO) classification system, there are three stages for angle closure glaucoma (ACG) ( Box 25.1 ):
- 1.
Primary angle closure suspect (PACS) is the term for an eye in which contact between the peripheral iris and posterior trabecular meshwork is considered possible, but there are no other abnormalities in the eye. There has been some debate recently regarding the diagnostic criteria for PACS. While 270° of iridotrabecular contact (where the posterior trabecular meshwork is not visible on gonioscopy) has been used as the minimum criterion for angle closure under the ISGEO system, this has been suggested to be too strict as eyes with lesser extent of closure may still have peripheral anterior synechiae (PAS). An alternative definition is one in which 180° is the cutoff for defining angle closure. Such a definition was recently used in population-based surveys in India and Singapore.
- 2.
Primary angle closure (PAC) is present when there are features in the eye indicating that trabecular meshwork obstruction by the peripheral iris has occurred. Such features include PAS, increased intraocular pressure (IOP), iris whorling, glaucomflecken ( Figure 25.1 ), lens opacities, or excessive pigment deposition on the trabecular meshwork. Importantly, the optic disc does not have signs of glaucomatous damage during this stage.
Figure 25.1
A slit-lamp photograph of an eye in acute angle closure. The pupil is mid dilated and there is glaucomflecken – ischemic anterior lens cortex fibers.
- 3.
PACG is PAC with evidence of glaucomatous optic neuropathy (GON) and visual field loss compatible with glaucoma.
| Primary angle closure suspect (PACS) |
|
| Primary angle closure (PAC) |
|
| Primary angle closure glaucoma (PACG) | • PAC with evidence of glaucomatous optic neuropathy |
Epidemiology
Age
The risk of angle closure increases with age. This appears to be due to progressive shallowing of the anterior chamber as the lens grows in thickness and moves forwards.
Ethnicity
The highest rates of ACG have been found in the Inuits. High rates of angle closure have also been described in East Asian populations from Mongolia, Singapore (Chinese), Myanmar and Hong Kong, and the rate is lower amongst Indians, Thais, and Malays. Several population-based studies have shown that the predominant form of ACG in Asia is asymptomatic and not acute angle closure. ACG prevalence is even lower amongst Europeans, with a prevalence of about 0.1% in people over 40 years. The fact that angle closure is more common among Chinese, even after adjusting for axial length and anterior-chamber depth (ACD), suggests that mechanisms for angle closure may differ across racial/ethnic groups, and that factors such as thicker iris or ciliary body anatomy may have an important role in causing the disease.
Clinical assessment
Gonioscopy
Gonioscopy is the main clinical method of assessing the angle. It visualizes the angle through a contact lens at the slit lamp. Various grading schemes categorize eyes on the basis of the width of the anterior-chamber angle. For example, the Spaeth classification assesses the insertion of the iris, the angular width of the angle recess, and the configuration of the peripheral iris. The Schaffer classification assesses the possibility of closure depending on which angle structures are visible ( Figure 25.2 ).
Peripheral anterior synechiae
PAS are present when the peripheral iris attaches anteriorly in the angle extending over the trabecular meshwork. PAS may be localized or extensive, pinpoint or broad. The ideal method to assess for PAS is dynamic indentation gonioscopy.
Anterior-segment optical coherence tomography (ASOCT) and ultrasound biomicroscopy (UBM)
AS-OCT and UBM are new and promising technologies for angle assessment. AS-OCT images the angle using infrared light in a noncontact fashion. Like the UBM, semiautomated image analyses can be performed. However, unlike the UBM it cannot image the ciliary body. The UBM requires a water bath to be placed on the eye of the supine patient before scanning occurs. Research comparing UBM, AS-OCT, and gonioscopy shows that AS-OCT and UBM are good at identifying narrow angles, but AS-OCT overidentifies subjects as having closed angles compared to gonioscopy.
Scanning peripheral anterior-chamber (SPAC) depth analyzer
The SPAC takes rapid slit measurements of the central and peripheral ACD which are compared to a normative database, and a risk assessment for angle closure is produced. SPAC is sensitive, but overestimates the proportion of narrow angles relative to gonioscopy and the modified van Herick grading system for peripheral ACD assessment.
Provocative testing
Provocation tests consist of placing subjects suspected as having angle closure into situations where there is a high chance of iridotrabecular contact. Examples include a dark room, prone positioning, and after pharmacologic pupil dilatation. However, provocative tests have not been shown to be consistently useful in correctly identifying those who are safe or at risk of angle closure.
Acute primary angle closure
Acute primary angle closure (APAC) presents with ocular pain, nausea and vomiting, intermittent blurring of vision with haloes noted around lights, and IOP usually much greater than 21 mmHg. Typically, there is marked conjunctival injection, corneal epithelial edema, a mid dilated unreactive pupil, a shallow anterior chamber, and the presence of a closed angle on gonioscopy ( Figure 25.3 ).
Treatment of angle closure glaucoma ( Box 25.2 )
Laser
Laser peripheral iridotomy (LPI)
The aim of an LPI is to eliminate pupil block. The iridotomy is usually placed between 11 and 1 o’clock so as to minimize visual disturbance. In thick brown irides, sequential use of argon laser to photocoagulate and pit the iris, and subsequent use of the Nd:YAG laser to create a patent hole has been described. In blue irides where less power is required, Nd:YAG laser may be all that is necessary. Postlaser IOP spikes can be alleviated by brimonidine or apraclonadine perioperatively.
Laser
Laser peripheral iridotomy (PI)
Argon laser peripheral iridoplasty
Medical therapy
Surgery
Trabeculectomy
Lens extraction for angle closure
Combined lens extraction and trabeculectomy surgery
If LPI fails or is unfeasible, surgical iridectomy may be pursued. No difference in terms of visual acuity or IOP has been observed between LPI and surgical iridectomy in a 3-year randomized controlled trial of unilateral APAC.
Studies have shown that 58% of APAC subjects need further treatment of some type whilst 32% need surgery after an APAC attack treated with LPI. However, for patients with chronic PACG, 90% of patients need medications or surgery after LPI.
Complications of LPI include increased IOP; laser burn to cornea, lens, or retina; development of posterior synechiae; and the development of a ghost image in the inferior field of vision. Other rare complications include progression of cataract opacity and corneal decompensation.
Argon laser peripheral iridoplasty
This may be indicated if the angle remains appositionally closed with high IOP. Iridoplasty involves the placement of circumferential low-energy laser burns which pull the adjacent iris out of the angle.
For cases of APAC, iridoplasty lessens the reliance on systemic medications which have side-effects, especially in elderly patients with systemic comorbidity. Medical therapy has a relatively slow onset, and 60% of APAC patients treated medically may still develop chronic PACG. In a randomized controlled trial from Hong Kong, iridoplasty was found to be better in reducing the IOP in the initial 2 hours after presentation of APAC . It was also found to lead to a low percentage of cases with subsequent PAS.
Medical therapy
Residual chronic PACG after iridectomy or iridotomy is common in Asian patients and is usually due to lens factors, plateau iris, or trabecular meshwork damage.
Topical beta-blockers, prostaglandin analogs, carbonic anhydrase inhibitors, and alpha-2-agonists can be used in angle closure patients in the same way as for primary open-angle glaucoma (POAG) management.
Latanoprost has been shown to be more effective than timolol in lowering IOP in Asian PACG eyes, even in eyes with 360° of PAS. Pilocarpine constricts the pupil and pulls the iris away from the trabecular meshwork. However, long-term use can result in posterior synechiae and can make cataract surgery more difficult. Miotic agents have not been shown to prevent progression of angle closure, and should not be used in place of an iridotomy.
Follow-up evaluation of treated PACG/APAC
Patients should have regular IOP checks (to detect asymptomatic rises in IOP) and indentation gonioscopy. Those with residual open angle after laser iridotomy and raised IOP and/or GON are managed similarly to those with POAG.
Plateau iris
Plateau iris is considered when the iris root is rotated forwards and centrally in a particular configuration. The iris surface is relatively flat and the anterior chamber is usually deep. The angle is narrow. Dynamic gonioscopy reveals a double-hump sign where the peripheral iris drapes over the anteriorly rotated ciliary processes. These patients tend to be female and younger and may have a family history of ACG. There is usually some element of pupil block. Cataract extraction may not be so useful in eyes with plateau iris as iridociliary apposition still occurs, whereas argon laser peripheral iridoplasty may be effective in opening up the angles.
Surgery
Trabeculectomy
Trabeculectomy is indicated when there is a failure of medical or laser treatment, or poor compliance or intolerance to medical treatment leading to poorly controlled glaucoma and continuing optic disc and visual field damage.
Lens extraction for angle closure
Lens extraction deepens the anterior chamber, decreases angle crowding, and relieves pupil block. Lai et al showed that this leads to a decrease in IOP, and a reduced requirement for antiglaucoma medications in PACG. Cataract surgery is technically difficult in PACG eyes because of frequently coexisting shallow anterior-chamber, large bulky lens, iris atrophy secondary to ischemia, and zonular weakness. This surgical option may be particularly useful in the setting of mild optic disc damage in PACG with coexisting cataract, but there is little evidence for its effectiveness in more severe cases of PACG.
Combined lens extraction and trabeculectomy surgery
This has been shown to have similar complication rates in PACG and POAG eyes and allows for an improvement in the visual acuity of PACG patients. Combined surgery may also prevent IOP spikes postoperatively and widens the angle.
Goniosynechialysis
This procedure involves stripping PAS from the angle wall, utilizing an instrument to peel PAS gently from the trabecular meshwork. However goniosynechialysis can cause IOP spikes, cataract, and hyphema. Goniosynechialysis can be combined with cataract surgery and has been found to be useful when PAS has been present for less than 1 year.
Management of acute primary angle closure
The main aims of APAC treatment are to reduce the IOP, reduce inflammation, and reverse the angle closure. The patient is kept supine to allow gravity to aid in posterior movement of the lens and be reassessed regularly. Analgesics and antiemetics are used for symptomatic relief.
Medical therapy includes some of the following agents, based on the patient’s overall medical status:
- •
Topical beta-adrenergic antagonists
- •
Topical alpha2-adrenergic agonists
- •
Topical or systemic carbonic anhydrase inhibitors
- •
Topical miotics
- •
Systemic hyperosmotic agents
Hyperosmotic agents such as mannitol 20% (or glycerol orally) can be used if the IOP remains high for too long. Hyperosmotic agents reduce vitreous volume by causing an osmotic diuresis. In one study, 44% of APAC patients required an osmotic agent to reduce IOP, sometimes in multiple administrations. Topical steroids should be used to reduce the sometimes marked inflammatory response.
The fellow eye of APAC requires prophylactic treatment with an LPI, since half of these will otherwise suffer an acute attack within 5 years.
Surgery for acute primary angle closure
Lens extraction for APAC
Lens removal serves to deepen the anterior chamber and open up the drainage angle. There is limited information whether primary cataract extraction as initial treatment is useful in APAC, but it is an option for refractory cases after attempting to break the pupillary block. The optimum timing of lens extraction in such cases is not known; the risks and technical difficulties of surgery have to be weighed against the need to reduce IOP.
Long-term prognosis after APAC
In one study, in the long term (4–10 years) following an APAC attack, 18% of eyes were blind, 48% of eyes developed serious GON, and 58% of eyes had vision worse than 20/40.
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